As is the case with all operating systems, DOS provides the basic foundation for the initialization of computer hardware for use by higher level software. In most cases DOS acts as the interface between the higher level software and the hardware. DOS based architecture and the architecture of IBM PC's, BIOS, and the Intel 80X series of chips has created some unique conditions which limit the robustness of the hardware not realized by other CPU architectures (Mainframe, Mini, RT, Mackintosh, Etc). One limitation is the recognition of only two (2) physical hard drives and two (2) floppy drives using standard DOS architecture.
FIG. 1 is a representation of the standard DOS architecture showing the DOS based computer (1D) with representations of its internal components. As displayed, the standard DOS disk input/output interface is allowing for information exchange between the two standard hard drive storage media, Drives 1-A and 2-A. The arrows represent direct communication between 1B and the Standard Drives. Computer Random Access Memory (RAM) is depicted by item 1C.
A drawback to data exchange between 1B and standard storage media is performance. The cause of this performance hit is the length of time it takes the storage media to retrieve or write the information after it gets the request. Prior art dramatically improved performance by implementing a "cache" in RAM. Caching is implemented between the standard DOS Disk I/O Interface (1B) and the Standard Drives (#1-A & #2-A). A cache acts as a reservoir for frequently requested information from the storage media. When a request comes from the computer (1D) to 1B, the cache implementation processes the request from 1B and checks to see if it already has the information from a previous request. If it does it supplies the information from the cache. Since the cache is an area of memory, it processes the request at a substantially faster rate than if the request would have gone through the routing of FIG. 1.
FIG. 2 is a representation of the system depicted in FIG. 1 with the incorporation of a standard cache (3C). The arrows represent the routing of information requests from 1B to 3C and then from 3C to 1-A and 2-A. The prior art of caching reserves a block of RAM (1C) for the storage of all files or pieces of files requested. Drawbacks are, that there is no mechanism which distinguishes files to be cached, and the memory used as the caching area cannot be used for other purposes by different software applications.
As has been intimated throughout this discussion, implementation of caches for standard drives are made through specific routes which process the standard requests.
FIG. 3, depicts the incorporation of a prior art RAM Disk (2C) into the standard architecture of FIG. 1. A RAM disk is a program which uses a block of RAM and turns it into a device which is recognized by DOS as a disk drive. Once established the RAM disk can be accessed (at the speed of memory) for many purposes by many different software applications, since it mimics standard storage devices. It is apparent from the previous discussion that this memory is distinctly different in characteristics as well as location, from the block of memory established for caching frequently requested information.
The limitation of the DOS based architecture to information routes to only two (2) standard hard drive storage devices, produced the need to find other routes for processing requests. Among these new prior art routes are the SCSI interface and the Local area network interface in DOS.
The SCSI interface was migrated to the PC level to provide new routes for accessing multiple and different types of data storage and retrieval devices. Devices such as CDROM (Compact Disk Read Only Memory), MOD (Magnetic Optical Disks {Read/Write}), WORM (Write Once Read Many), Jute Boxes (Robotic mechanism for automatically changing disks without user intervention these can be both ROM & WORM drives), Bernoulli and tape subsystems, could be simultaneously attached to the Standard DOS Disk I/O, and appear as another drive to the system. FIG. 4 depicts this additional SCSI route and a number of Non-Standard storage devices (Drive 1E.gtoreq.4E).
FIG. 4 depicts a RAM disk (2C) in addition to the standard cache routing depicted in FIG. 3. Please note the distinct routing and memory area used for standard cache implementation.
Similarly, the DOS Local Area Network interface (LAN) allows sharing hard drives of a file server in a client server LAN, or the hard drives of a neighboring computer in a DOS based pear-to-pear LAN, through another distinct route. As was the case for the DOS SCSI interface, this provide new routes for accessing multiple and different types of data storage and retrieval devices physically located in different computers.
FIG. 5 is identical to FIG. 4 except, it is illustrative of the distinct nature of the Network (LAN) route for information requests.
The additional routing methods of prior art are not exclusive in nature due to their distinct implementation, and resultant routes.
FIG. 6 depicts the incorporation of both DOS SCSI and LAN routes incorporated into a single computer (1D).
FIG. 4 through FIG. 6 inclusive, are illustrative of the prior art caching implementations use within the standard DOS drive route only. Current caching techniques to date, have been ineffectual on additional routings which have been implemented.
Caching becomes very important with regard to these additional routes, since typical information retrieval times are slower through these routes than uncached standard hard drives.